fix hotspot build failures with -D_FORTIFY_SOURCE=2 and -Wformat=1

[Andrew Haley]

Kelly O'Hair wrote:
> Both fwrite() and (void)fwrite() are legal,
> the first one is a potential error, but the later
> is defined by the standard as having the function return value
> explicitly "discarded".

The standard doesn't distinguish between them.  Both are evaluated
as void expressions.

> So warning about a value that has been explicitly "discarded" by
> the terms of the standard seems like a very questionable warning.

Perhaps so, but that is nothing to do with standards conformance,
which you were questioning.  Let me be clear: a C compiler is allowed
to warn about anything at all, as long as every standard program is
executed according to the rules of the abstract machine.

Andrew.


> Andrew Haley wrote:
>> Kelly O'Hair wrote:
>>> The issue seems so simple to me.
>>> If the function return is to be ignored, you make an explicit cast
>>> to void. This practice is so old and common I don't understand why
>>> it's so complicated.
>>
>>> gcc/g++ are not the only compilers on the planet.
>>> Writing portable C or C++ code becomes increasingly more complicated
>>> when you have to rely on special features of the compiler to get them
>>> to shut up about perfectly valid code.
>>>
>>> What happened to following the standards?
>>>
>>> WG14/N1124 6.3.2.2 void
>>>
>>> "... If an expression of any other type is evaluated as a void
>>> expression, its value or designator is discarded.
>>> (A void expression is evaluated for its side effects.)"
>>
>> Huh?  The standard doesn't say that you should not warn about
>> legal but potentially problematic code.  That's what most
>> warnings are, after all.
>>
>> Andrew.